Linux Virtualization - May 2020 - [EXT] Re: [PATCH v5] iommu/virtio: Use page size bitmap supported by endpoint

On Wed, May 13, 2020 at 09:15:22AM +0000, Bharat Bhushan
wrote:
> Hi Jean,
> 
> > -----Original Message-----
> > From: Michael S. Tsirkin <mst at redhat.com>
> > Sent: Wednesday, May 6, 2020 5:53 AM
> > To: Bharat Bhushan <bbhushan2 at marvell.com>
> > Cc: jean-philippe at linaro.org; joro at 8bytes.org; jasowang at
redhat.com;
> > virtualization at lists.linux-foundation.org; iommu at
lists.linux-foundation.org;
> > linux-kernel at vger.kernel.org; eric.auger.pro at gmail.com;
eric.auger at redhat.com
> > Subject: [EXT] Re: [PATCH v5] iommu/virtio: Use page size bitmap
supported by
> > endpoint
[...]
> > > +struct virtio_iommu_probe_pgsize_mask {
> > > +	struct virtio_iommu_probe_property	head;
> > > +	__u8					reserved[4];
> > > +	__le64					pgsize_bitmap;
> > > +};
> > > +
> > 
> > This is UAPI. Document the format of pgsize_bitmap please.
> 
> I do not see uapi documentation in "Documentation" folder of
other data struct in this file, am I missing something?
I'm not the one requesting this change, but I'm guessing you should add
a
comment in this header, above pgsize_bitmap (which should actually be
called page_size_mask to follow the spec). I guess I'd add:

/* Same format as virtio_iommu_config::page_size_mask */

for this field, and then maybe change the comment of virtio_iommu_config,
currently "/* Supported page sizes */", to something more precise such
as:

/*
 * Bitmap of supported page sizes. The least significant bit indicates the
 * smallest granularity and the other bits are hints indicating optimal
 * block sizes.
 */

But I don't know how much should be spelled out here, since those details
are available in the spec.

Thanks,
Jean